1. Field of the Invention
The present invention relates to a laser apparatus, and more particularly, to apparatus which includes a compact pulsed dye laser for high pulse repetition frequency (prf) operation.
2. State of the Prior Art.
Dye lasers are particularly advantageous for certain laser applications because they can provide output wavelengths over relatively large segments of the visible spectrum. This is in contrast to most lasers which are only capable of providing strong output wavelengths at a limited number of discrete wavelengths. In all lasers, the active lasing material must be "pumped" to elevated excitation levels. In the case of a dye laser, this pumping excitation is accomplished optically. That is, energy in the form of electromagnetic energy in the optical region of the spectrum is directed at the dye. This includes not only energy in the visible part of the electromagnetic spectrum, but, also, energy in the infrared and ultraviolet portions of the spectrum.
In U. S. Pat. No, 4,013,978, there is disclosed a dye laser for use in photocoagulation therapy in which a solution of active dye is pumped through a cell. The cell is closed at one end by a polished stainless steel sheet and at an opposite end by a partially-silvered mirror which forms the outlet window. Dye solution from a reservoir is slowly circulated through the cell to produce a gradual change of the dye solution in the cell and to equalize the temperature difference between the solution in the cell and the reservoir. Flash tubes on opposite sides of the cell are energizable to optically pump the cell, that is to stimulate emission of radiation in the active material in the cell. A problem with this dye laser is that the flashlamps are operated at a frequency which is too low for many applications. Further, if an attempt were made to operate the apparatus at a higher frequency, the slowly-circulating dye solution would be heated to a point where chemical breakdown of the dye would occur.
A copper laser-pumped dye laser which operates at a high prf is disclosed in an article entitled "Narrow linewidth, high prf copper laser-pumped dye-laser oscillators, " by F. J. Duarte and J. A. Piper, Applied Optics, Vol. 23, No. 9, May 1, 1984. This laser utilizes a dye cell which is triangular in cross section, and dye solution is circulated through the cell at a velocity of approximately 5 msec.sup.-1 in a direction transverse to the optical axis. The copper vapor laser, used as the pump source, was operated to produce pump pulses of 20-30 nsec in duration. Although such a device is capable of high performance, it has been recognized that it would be desirable to operate at even higher pulse repetition frequencies. For example, in applications such as spectroscopy, the faster the pulse rate the faster data can be collected.